Instantaneous hot water heaters are well known in the art, and are exemplified, for example, by the disclosures in U.S. Pat. Nos.: 987,658; 1,362,356; 1,738,360; 1,827,639; 1,941,584; 1,952,774; 2,807,702; and 4,119,833. The prior art heaters are unduly complicated and comprise many different parts or components which render them expensive to manufacture and difficult to assemble. Also, the complexities of such heaters make them susceptible to malfunctioning or water leakage.